The comeback story of U.S. Rep. Gabrielle Giffords took an emotional turn Sunday as the wounded congresswoman announced she would resign to dedicate her full attention to rehabilitation.

In a two-minute YouTube video, Giffords referenced her traumatic brain injury, announced her planned resignation and expressed her hope for unity and progress in government.

“A lot has happened over the past year,” she said. “We cannot change that. But I know on the issues we fought for, we can change things for the better.”

Giffords, 41, was shot in the head on Jan. 8, 2011, in a Tucson rampage that left six dead and 12 others wounded. The Arizona congresswoman spent most of the last year undergoing treatment and rehabilitation in Houston and League City, where she now lives with her husband, former astronaut Mark Kelly.

Giffords said her decision to resign was in the interest of her home state.

“I have more work to do on my recovery, so to do what is best for Arizona, I will step down this week.”

Giffords’ broken speech was evident in the video, which conveyed her message through a series of clips that appeared spliced together. She wore a red jacket and appeared without glasses, which she has worn regularly since her eyesight was substantially damaged in the shooting. She ended with a promise.

“I’m getting better,” she said. “Every day, my spirit is high. I will return and we will work together for Arizona and this great country.”

Back to Washington

In one of her final acts as a congresswoman, Giffords will attend President Barack Obama‘s State of the Union speech Tuesday in Washington. She will not seek re-election in November, according to her office.

Her resignation will prompt Arizona Gov. Jan Brewer to call a special election to fill her seat until the term expires in January 2013 and will throw her conservative-leaning Arizona congressional district into contention. It will also mean the loss of one of the most moderate and collaborative representatives on Capitol Hill, friends said.

Giffords’ decision was also a powerful choice that would be best for her constituents and recovery, they said.

“It’s a really selfless decision, if you think about it,” said Rep. Debbie Wasserman Schultz, D-Fla., one of Giffords’ closest friends on Capitol Hill.

Full representation

Giffords struggled with the decision to resign and had been focused on working toward a return to Congress. But after her recent trip to Tucson for the anniversary of the Jan. 8 shooting, she realized that the re-election campaign would arrive quickly and not allow her to focus as much on recovery, Wasserman Schultz said.

“It was a tough decision and I think she went through the range of emotions, but she’s at peace with the decision,” she said.

Giffords felt it was important for her constituents to have full representation in Congress as soon as possible, Wasserman Schultz said.

Rep. Ted Poe, R-Humble, who worked with Giffords and her office on efforts to improve border security, said Giffords’ example for bipartisan cooperation would be missed in Congress.

“She was issue-oriented and partisanship was never an issue,” he said.

Rep. Pete Olson, R-Sugar Land, worked with Giffords on the House subcommittee overseeing NASA, over which she was the chairwoman. He said Giffords was a tenacious congresswoman whom he expected to return to public service.

Giffords was in Tucson on Sunday and “looked great,” said Arizona State Sen. Linda Lopez, a close friend who was pleased to see the pressure of a possible re-election campaign out of the picture.

“A wave of relief went over me,” Lopez said of hearing about Giffords’ decision to resign. “It just feels so good to know that now she can focus on getting better and having a life and focusing on her recovery and not have to worry about thinking about ‘Is she going to go back?’ or ‘Can she go back?’?”

“Gabby Giffords embodies the very best of what public service should be,” Obama said. “She’s universally admired for qualities that transcend party or ideology – a dedication to fairness, a willingness to listen to different ideas, and a tireless commitment to the work of perfecting our union.”

Despite speculation that Giffords’ husband, Kelly, would seek to replace her by running for her seat, friends said he had made no plans to do so.

Among Giffords’ plans before her resignation will be a trip to the Tucson supermarket where she was shot. Giffords will attempt to finish the “Congress On Your Corner” event that was interrupted by the shooting a year ago and plans to meet attendees from that day at the supermarket, according to her office.